Stone Processing            

Quarry and Quarrying, open excavation from which any useful stone is extracted for building and engineering purposes, and the operations required to obtain rock in useful form from a quarry. The two principal branches of the industry are the so-called dimension-stone and crushed-stone quarrying. In the former, blocks of stone, such as marble, are extracted in different shapes and sizes for different purposes. In the crushed-stone industry, granite, limestone, sandstone, or basaltic rock are crushed for use principally as concrete aggregate or roadstone.

Quarrying is carried out by different methods and equipment, such as hand tools, explosives, or power saws, and by channeling and wedging, according to the purpose for which the stone is extracted. Hand tools alone may be used for quarrying stone that lies in easily accessible beds. The principal hand tools are the drill, hammer, and wedge. A row of holes several centimeters apart is made with the drill and the hand hammer, partly through the layer, or stratum, perpendicular to its plane of stratification and along the line at which it is desired to break the stone. Each hole in a long row is filled with three wedges, shaped so that one may be driven down through the others, the method being known as plug and feathers; by striking each plug a sharp blow with a hammer, hitting them in succession, and by repeating the operation several times, the combined splitting force of the plugs and feathers finally becomes great enough to rupture the rock.

Explosives are most commonly employed for detaching large blocks of stone, which are then split and broken into smaller stones by wedges or by the plug-and-feathers method, or crushed by a heavy steel ball weighing several tons. In this method of quarrying, the drill holes are put down to the depth to which it is required to break the rock and are then partly filled with some explosive that is discharged by the usual methods of blasting. To obtain finely crushed stones for concrete, primary crushers, of the jaw or gyratory type, and secondary crushers are used to reduce the size of the rocks.

Channeling is the process of cutting long, narrow channels in rock to free the sides of large blocks of stone. Channeling machines, or channelers, formerly steam driven, have now been generally replaced by gasoline or electric engines. These are self-propelling and move a cutting edge back and forth along the line on a rock bed on which the channel cut is to be made. The channel cut is sunk deep enough to permit the insertion of wedges by which the rock is split, the cut or groove guiding the fracture. The channeling and wedging process of quarrying is extensively used in quarrying marble, sandstone, limestone, and the other softer rocks, but is not successful for granite and other hard rocks.

Another method of cutting is by the combination of a power saw, an abrasive, and water as a lubricant and a coolant. The saw cuts a narrow channel, the primary or initial cut, that is then either expanded by a wedge or is blasted. This method is used in slate, granite, and limestone quarries.

An automatic channel burner has recently come into commercial use in dimension-stone quarrying. It resembles a handheld burner held vertically in a frame, with an electric motor moving the whole unit slowly down a track. It makes a more even cut, does not require the presence of an operator, and wastes less rock. The unit is controlled by a computer.

In 1988, approximately 1.159 million short tons of dimension stone were produced, mostly for buildings, monuments, and as curbing. In comparison, 1.25 billion short tons of crushed stone were produced, with three-quarters of that being limestone and dolomite.